Multiple-frequency calibration of two-dimensional hydrophone arrays for instantaneous beam width measurements of shock-wave lithotripters

Characterizations of electrohydraulic lithotripters (EHLs) are usually limited to single-point measurements because hydrophone arrays are not readily available, or are prohibitively expensive. Furthermore, beamwidth measurements of peak pressure values made with single-point hydrophones are inaccurate. This inaccuracy comes from the high variability of the acoustic field and the fact that several shocks must be averaged to create a single beamwidth profile when using single-element hydrophones. Previous work demonstrated that characterizing the beam of an EHL with a single-point measurement technique led to an overestimate error of 25% compared to an instantaneous beamwidth measurement using a linear hydrophone array. In this paper, the improvement of our disposable, repeatable, hydrophone array is presented. The geometry was changed to that of a two-dimensional hydrophone array, which allows for the measurement of the instantaneous acoustic field of an EHL and its variation in 2-D. Modifications were made to the hydrophone fabrication methods which improved sensitivity and performance. Finally, a multiple-frequency calibration technique was implemented, allowing absolute pressures to be obtained for each hydrophone element.